(1) Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly to a static type semiconductor memory device having a flash-clear function.
(2) Description of the Related Art
In a conventional static type semiconductor memory device, each memory cell is constituted by two inverters, and these memory cells are arranged in a matrix form so that reading or writing of data can be made to any one particular memory cell selected from the matrix. The semiconductor memory device constituting a cache memory is capable of simultaneously rewriting or renewing the data of a plurality of memory cells with the same data. Thus, the two inverters constituting each of the memory cells are constructed with inherent characteristic differences, meaning that each flip-flop can be easily brought to a predetermined state so that the writing of data to a plurality of memory cells can be performed simultaneously.
For example, in the conventional flip-flop shown in FIG. 1, the resistance values of the resistors R1 and R2 are set for R1&gt;R2, so that the transistor Q1 of the two transistors constituting the flip-flop may easily turn ON. Thus, when the data holding function of the memory cells is reactivated after having been temporarily stopped, the data in the plurality of memory cells can be simultaneously rewritten or renewed with the same data.
However, there has been a problem with the kind of conventional semiconductor memory device described above that, since the characteristics of the memory cells tend to lean to one particular state of the two, differences are caused to occur in the writing-in characteristics in the normal use of the device or differences are caused to occur in data holding characteristics. This is a problem with the conventional semiconductor memory devices which is to be solved by the present invention.